UUMMM. I thought I answered that in the wording of my last post, I don't think you could call it 'NORMAL'. But, it does happen and way too often.
Part of the question becomes how you want to define 'Testing Facilities'? If you mean ATF's, then it would be very uncommon. But still happens. Too little training of personnel at SOME of them. Hopefully they get it caught and taken care of at any audits. BUT...??? Who knows.
But, are you also including one man operation CWI's who qualify welders to make their living when you say 'Testing Facilities'? Then the numbers go up in my personal opinion and experience.
Now, there is a third class, Testing Companies who have a lot of good and expensive equipment and people who do everything from soils, to concrete, to welding, to ... you name it. They test it. RT, UT, MT, PT, Macro etching, bending, pulling, they do it. Most of them have very good reputations. They can make mistakes. They do hire new people and sometimes the learning curve lets less than perfect results happen.
If you want numbers, ratios, percentages, NOPE, can't and won't even try to GUESS. All I can say is IT HAPPENS. And once is too often in a perfect world. But even the codes acknowledge a less than perfect work environment. Look at arc strikes. They are to be avoided. Reference an article I wrote in IT about them a couple of years ago. The codes tell us how to deal with those occasions when the less than perfect happens. It does not strictly prohibit and make rejectable every piece that this happens to. If it did, we would never complete a building.
Bottom line, I would say, PLAINLY, IT IS NOT NORMAL. But, it happens.
He Is In Control, Have a Great Day, Brent